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[PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning

guoren@kernel.org posted 11 patches 3 years, 6 months ago
There is a newer version of this series
[PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning
Posted by guoren@kernel.org 3 years, 6 months ago 
From: Guo Ren <guoren@linux.alibaba.com>

When DEBUG_PREEMPT=y,
	exit_to_user_mode_prepare
	->tick_nohz_user_enter_prepare
	  ->tick_nohz_full_cpu(smp_processor_id())
	    ->smp_processor_id()
	      ->debug_smp_processor_id()
		->check preempt_count() then:

[    5.717610] BUG: using smp_processor_id() in preemptible [00000000]
code: S20urandom/94
[    5.718111] caller is debug_smp_processor_id+0x24/0x38
[    5.718417] CPU: 1 PID: 94 Comm: S20urandom Not tainted
6.0.0-rc3-00010-gfd0a0d619c63-dirty #238
[    5.718886] Hardware name: riscv-virtio,qemu (DT)
[    5.719136] Call Trace:
[    5.719281] [<ffffffff800055fc>] dump_backtrace+0x2c/0x3c
[    5.719566] [<ffffffff80ae6cb0>] show_stack+0x44/0x5c
[    5.720023] [<ffffffff80aee870>] dump_stack_lvl+0x74/0xa4
[    5.720557] [<ffffffff80aee8bc>] dump_stack+0x1c/0x2c
[    5.721033] [<ffffffff80af65c0>]
check_preemption_disabled+0x104/0x108
[    5.721538] [<ffffffff80af65e8>] debug_smp_processor_id+0x24/0x38
[    5.722001] [<ffffffff800aee30>] exit_to_user_mode_prepare+0x48/0x178
[    5.722355] [<ffffffff80af5bf4>] irqentry_exit_to_user_mode+0x18/0x30
[    5.722685] [<ffffffff80af5c70>] irqentry_exit+0x64/0xa4
[    5.722953] [<ffffffff80af52f4>] do_page_fault+0x1d8/0x544
[    5.723291] [<ffffffff80003310>] ret_from_exception+0x0/0xb8

(Above is found in riscv platform with generic_entry)

The smp_processor_id() needs irqs disable or preempt_disable, so use
preempt dis/in protecting the tick_nohz_user_enter_prepare().

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 kernel/entry/common.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 063068a9ea9b..36e4cd50531c 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -194,8 +194,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
 
 	lockdep_assert_irqs_disabled();
 
+	preempt_disable();
 	/* Flush pending rcuog wakeup before the last need_resched() check */
 	tick_nohz_user_enter_prepare();
+	preempt_enable();
 
 	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
 		ti_work = exit_to_user_mode_loop(regs, ti_work);
-- 
2.36.1
Re: [PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning
Posted by Peter Zijlstra 3 years, 6 months ago 
On Sun, Sep 18, 2022 at 11:52:41AM -0400, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> When DEBUG_PREEMPT=y,
> 	exit_to_user_mode_prepare
> 	->tick_nohz_user_enter_prepare
> 	  ->tick_nohz_full_cpu(smp_processor_id())
> 	    ->smp_processor_id()
> 	      ->debug_smp_processor_id()
> 		->check preempt_count() then:
> 
> [    5.717610] BUG: using smp_processor_id() in preemptible [00000000]
> code: S20urandom/94
> [    5.718111] caller is debug_smp_processor_id+0x24/0x38
> [    5.718417] CPU: 1 PID: 94 Comm: S20urandom Not tainted
> 6.0.0-rc3-00010-gfd0a0d619c63-dirty #238
> [    5.718886] Hardware name: riscv-virtio,qemu (DT)
> [    5.719136] Call Trace:
> [    5.719281] [<ffffffff800055fc>] dump_backtrace+0x2c/0x3c
> [    5.719566] [<ffffffff80ae6cb0>] show_stack+0x44/0x5c
> [    5.720023] [<ffffffff80aee870>] dump_stack_lvl+0x74/0xa4
> [    5.720557] [<ffffffff80aee8bc>] dump_stack+0x1c/0x2c
> [    5.721033] [<ffffffff80af65c0>]
> check_preemption_disabled+0x104/0x108
> [    5.721538] [<ffffffff80af65e8>] debug_smp_processor_id+0x24/0x38
> [    5.722001] [<ffffffff800aee30>] exit_to_user_mode_prepare+0x48/0x178
> [    5.722355] [<ffffffff80af5bf4>] irqentry_exit_to_user_mode+0x18/0x30
> [    5.722685] [<ffffffff80af5c70>] irqentry_exit+0x64/0xa4
> [    5.722953] [<ffffffff80af52f4>] do_page_fault+0x1d8/0x544
> [    5.723291] [<ffffffff80003310>] ret_from_exception+0x0/0xb8
> 
> (Above is found in riscv platform with generic_entry)
> 
> The smp_processor_id() needs irqs disable or preempt_disable, so use
> preempt dis/in protecting the tick_nohz_user_enter_prepare().
> 
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
>  kernel/entry/common.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 063068a9ea9b..36e4cd50531c 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -194,8 +194,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
>  
>  	lockdep_assert_irqs_disabled();

    Observe ^^^^

>  
> +	preempt_disable();
>  	/* Flush pending rcuog wakeup before the last need_resched() check */
>  	tick_nohz_user_enter_prepare();
> +	preempt_enable();

This makes no sense; if IRQs are disabled, check_preemption_disabled()
should bail early per:

	if (irqs_disabled())
		goto out;
Re: [PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning
Posted by Guo Ren 3 years, 6 months ago 
On Mon, Sep 19, 2022 at 7:59 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sun, Sep 18, 2022 at 11:52:41AM -0400, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > When DEBUG_PREEMPT=y,
> >       exit_to_user_mode_prepare
> >       ->tick_nohz_user_enter_prepare
> >         ->tick_nohz_full_cpu(smp_processor_id())
> >           ->smp_processor_id()
> >             ->debug_smp_processor_id()
> >               ->check preempt_count() then:
> >
> > [    5.717610] BUG: using smp_processor_id() in preemptible [00000000]
> > code: S20urandom/94
> > [    5.718111] caller is debug_smp_processor_id+0x24/0x38
> > [    5.718417] CPU: 1 PID: 94 Comm: S20urandom Not tainted
> > 6.0.0-rc3-00010-gfd0a0d619c63-dirty #238
> > [    5.718886] Hardware name: riscv-virtio,qemu (DT)
> > [    5.719136] Call Trace:
> > [    5.719281] [<ffffffff800055fc>] dump_backtrace+0x2c/0x3c
> > [    5.719566] [<ffffffff80ae6cb0>] show_stack+0x44/0x5c
> > [    5.720023] [<ffffffff80aee870>] dump_stack_lvl+0x74/0xa4
> > [    5.720557] [<ffffffff80aee8bc>] dump_stack+0x1c/0x2c
> > [    5.721033] [<ffffffff80af65c0>]
> > check_preemption_disabled+0x104/0x108
> > [    5.721538] [<ffffffff80af65e8>] debug_smp_processor_id+0x24/0x38
> > [    5.722001] [<ffffffff800aee30>] exit_to_user_mode_prepare+0x48/0x178
> > [    5.722355] [<ffffffff80af5bf4>] irqentry_exit_to_user_mode+0x18/0x30
> > [    5.722685] [<ffffffff80af5c70>] irqentry_exit+0x64/0xa4
> > [    5.722953] [<ffffffff80af52f4>] do_page_fault+0x1d8/0x544
> > [    5.723291] [<ffffffff80003310>] ret_from_exception+0x0/0xb8
> >
> > (Above is found in riscv platform with generic_entry)
> >
> > The smp_processor_id() needs irqs disable or preempt_disable, so use
> > preempt dis/in protecting the tick_nohz_user_enter_prepare().
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> >  kernel/entry/common.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> > index 063068a9ea9b..36e4cd50531c 100644
> > --- a/kernel/entry/common.c
> > +++ b/kernel/entry/common.c
> > @@ -194,8 +194,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
> >
> >       lockdep_assert_irqs_disabled();
>
>     Observe ^^^^
Thanks! I would enable PROVE_LOCKING for test.

>
> >
> > +     preempt_disable();
> >       /* Flush pending rcuog wakeup before the last need_resched() check */
> >       tick_nohz_user_enter_prepare();
> > +     preempt_enable();
>
> This makes no sense; if IRQs are disabled, check_preemption_disabled()
> should bail early per:
>
>         if (irqs_disabled())
>                 goto out;
Ditto.


-- 
Best Regards
 Guo Ren
Re: [PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning
Posted by Guo Ren 3 years, 6 months ago 
On Tue, Sep 20, 2022 at 9:45 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Mon, Sep 19, 2022 at 7:59 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Sun, Sep 18, 2022 at 11:52:41AM -0400, guoren@kernel.org wrote:
> > > From: Guo Ren <guoren@linux.alibaba.com>
> > >
> > > When DEBUG_PREEMPT=y,
> > >       exit_to_user_mode_prepare
> > >       ->tick_nohz_user_enter_prepare
> > >         ->tick_nohz_full_cpu(smp_processor_id())
> > >           ->smp_processor_id()
> > >             ->debug_smp_processor_id()
> > >               ->check preempt_count() then:
> > >
> > > [    5.717610] BUG: using smp_processor_id() in preemptible [00000000]
> > > code: S20urandom/94
> > > [    5.718111] caller is debug_smp_processor_id+0x24/0x38
> > > [    5.718417] CPU: 1 PID: 94 Comm: S20urandom Not tainted
> > > 6.0.0-rc3-00010-gfd0a0d619c63-dirty #238
> > > [    5.718886] Hardware name: riscv-virtio,qemu (DT)
> > > [    5.719136] Call Trace:
> > > [    5.719281] [<ffffffff800055fc>] dump_backtrace+0x2c/0x3c
> > > [    5.719566] [<ffffffff80ae6cb0>] show_stack+0x44/0x5c
> > > [    5.720023] [<ffffffff80aee870>] dump_stack_lvl+0x74/0xa4
> > > [    5.720557] [<ffffffff80aee8bc>] dump_stack+0x1c/0x2c
> > > [    5.721033] [<ffffffff80af65c0>]
> > > check_preemption_disabled+0x104/0x108
> > > [    5.721538] [<ffffffff80af65e8>] debug_smp_processor_id+0x24/0x38
> > > [    5.722001] [<ffffffff800aee30>] exit_to_user_mode_prepare+0x48/0x178
> > > [    5.722355] [<ffffffff80af5bf4>] irqentry_exit_to_user_mode+0x18/0x30
> > > [    5.722685] [<ffffffff80af5c70>] irqentry_exit+0x64/0xa4
> > > [    5.722953] [<ffffffff80af52f4>] do_page_fault+0x1d8/0x544
> > > [    5.723291] [<ffffffff80003310>] ret_from_exception+0x0/0xb8
> > >
> > > (Above is found in riscv platform with generic_entry)
> > >
> > > The smp_processor_id() needs irqs disable or preempt_disable, so use
> > > preempt dis/in protecting the tick_nohz_user_enter_prepare().
> > >
> > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > ---
> > >  kernel/entry/common.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> > > index 063068a9ea9b..36e4cd50531c 100644
> > > --- a/kernel/entry/common.c
> > > +++ b/kernel/entry/common.c
> > > @@ -194,8 +194,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
> > >
> > >       lockdep_assert_irqs_disabled();
> >
> >     Observe ^^^^
> Thanks! I would enable PROVE_LOCKING for test.
It's my bug in page_fault, here is the solution:

@@ -358,6 +358,8 @@ asmlinkage void noinstr do_page_fault(struct pt_regs *regs)

        __do_page_fault(regs);

+       local_irq_disable();
+
        irqentry_exit(regs, state);
 }
 NOKPROBE_SYMBOL(do_page_fault);

>
> >
> > >
> > > +     preempt_disable();
> > >       /* Flush pending rcuog wakeup before the last need_resched() check */
> > >       tick_nohz_user_enter_prepare();
> > > +     preempt_enable();
> >
> > This makes no sense; if IRQs are disabled, check_preemption_disabled()
> > should bail early per:
> >
> >         if (irqs_disabled())
> >                 goto out;
> Ditto.
>
>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren

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